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Investigating coronal saturation and supersaturation in fast-rotating M-dwarf stars

Jeffries, R. D. ; Jackson, R. J. ; Briggs, K. R. ; Evans, P. A. ; Pye, J. P.

In: Monthly Notices of the Royal Astronomical Society, 2011, vol. 411, no. 3, p. 2099-2112

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    Titel
    • Investigating coronal saturation and supersaturation in fast-rotating M-dwarf stars
    Autor
    • Jeffries, R. D.. Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Staffordshire ST5 5BG
    • Jackson, R. J.. Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Staffordshire ST5 5BG
    • Briggs, K. R.. ETH Zurich, Institute of Astronomy, 8093 Zurich, Switzerland
    • Evans, P. A.. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH
    • Pye, J. P.. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH
    Dokumententyp
    • Postprint
    Sprache
    • Englisch
    Veröffentlicht in
    • Monthly Notices of the Royal Astronomical Society, 2011, vol. 411, no. 3, p. 2099-2112. Blackwell Publishing Ltd
    Andere elektronische Ausgabe
    OAI-PMH-ID
    • oai:doc.rero.ch:304764
    Summary
    At fast rotation rates, the coronal activity of G- and K-type stars has been observed to ‘saturate' and then decline again at even faster rotation rates - a phenomenon dubbed ‘supersaturation'. In this paper, we investigate coronal activity in fast-rotating M-dwarfs using deep XMM-Newton observations of 97 low-mass stars of known rotation period in the young open cluster NGC 2547 and combine these with published X-ray surveys of low-mass field and cluster stars of known rotation period. Like G- and K-dwarfs, we find that M-dwarfs exhibit increasing coronal activity with decreasing Rossby number NR, the ratio of period to convective turnover time, and that activity saturates at LX/Lbol≃ 10−3 for log NR < −0.8. However, supersaturation is not convincingly displayed by M-dwarfs, despite the presence of many objects in our sample with log NR < −1.8, where supersaturation is observed to occur in higher mass stars. Instead, it appears that a short rotation period is the primary predictor of supersaturation; P ≤ 0.3 d for K-dwarfs and perhaps P ≤ 0.2 d for M-dwarfs. These observations favour the ‘centrifugal stripping' model for supersaturation, where coronal structures are forced open or become radiatively unstable as the Keplerian corotation radius moves inside the X-ray-emitting coronal volume